(1) Yes, the water moving up the face of a wave, is a major driving force in producing board speed on the face of a wave.
(2) My fins DO obey the laws of physics. As do ALL fins.
(3) I abhor flex! The much worshiped ‘‘twang’’ returns less energy than was used to flex and load the fin, producing a net loss in speed and performance.
(4) I bought into flex, in the mid 60’s. Would it surprise you to know that a flex fins produce subsonic occillations/vibrations that dramatically reduce board speed? This from direct observation, in perfect 20 foot Makaha waves, on a gun with a flex fin. The board would go slower and slower, in trim, as the wave got steeper and steeper. It was then that the fin vibration could be felt, through my back foot, though it was inaudible. that is when the lightbulb went on! Flex sucks! Stiff well foiled fins DO NOT do that. This also, from direct observation, and experience in significant waves.
(5) Yes. HINT: The basis of the secret foil, is found in nature, IF you know where to look. And, most importantly, IF you understand what you are looking at.
Perhaps you could enlighten us. Please explain the physics involved when increasing speed by inreasing drag. Maybe you could tell us how you as professional board builder would solve this design challenge for physics.
Ok my favourite single fin for all my boards is a narrow base 9.75 with extra rake mounted back in the box… Tried the pivots, cut aways with side bites, etc. What I like is loose drive with side slip that won’t spin out. I hate a stiff boards. Basically a flex fin is what im describing. Bill would your “thicker cord foil” enhance a flex fin template?
It would be very helpful if I knew the dimensions of the narrow base, you described. I’m going to assume that the fin is a fairly high aspect ratio fin. Also, is the 9.75 inches the vertical depth, or the length of the fin? Here has been my experience. A very high aspect ratio fin, in slower smaller waves, feels loose, and is easily ‘‘broken loose’’ into a sideslip. Typically a longer base, is part of the ‘‘cure’’, if that is what you’re after. Addressing your question, yes a thicker foil, with more surface camber, will greatly improve the performance of the fin you’ve described. You will experience, what feels like, an increase of speed through turns. It’s actually a case of not bleeding off speed due to fin stall, the increased foil efficiency carries more speed into your next maneuver. You also tap more of the wave energy, especially noticable in backside cutbacks, and trimming the high line in larger waves.
Hey Bill, I reckon not only does it feel like it’s going faster through turns, in the right conditions there is definitely acceleration. Physics at work.
Pressure from your weight on your legs on the board bottom of the board combined with the working side of the fin to stop the board slipping out, done properly, should produce forward energy.
The main variable that helped this work for me was a decent fin depth. I only ever got real acceleration using deeper fins, while I found the shallower, smaller, lower aspect fins are perfect for the slipping sensation, pretty much feeling fast, but mimicking speed with a certain amount of slide, and a certain amount of lack of grip.
Prove it, either mathematically or diagramatically or any other way, but otherwise all the above remains little more than conjecture and hypothosis.
By the way the vibration sounds like some sort of flutter/stall/turbulent hydro-elastic decompression/load shedding/ re-loading thing. Too much flex and not enough area.
The video posted earlier offered a simple solution to quantify speed. Attach a GPS device to a given board that has been equipped with any fin design of interest and synchronize it with a digital video recording of the ride. There will be some rider wave variability but points of speed increase and decrease should be simple to identify/pinpoint. Speed for “many” waves could be collected for each fin of interest and compared.
GPS and digital video technology is readily available and simple to use. Accuracy and precision of the GPS device and video equipment can be selected and evaluated, calibrating on land prior to surfboard testing.
EDIT: Without data, performance is speculation**…**
If GPS was used, if would have to be mounted to the center of the board. Otherwise every swing of nose or tail would be reflected in the speed number even though the board speed may actually decrease. Easy to measure straight line speed, but Bill is claiming increased spped while turning.
I do not believe gyrations of only a few feet will have any significant influence on the speed measurement. “Centripetal acceleration (turns)” does not increase speed – it is the change in “velocitiy (not speed)” caused by “change in direction.”
Nonetheless, the GPS device could be mounted/embedded in the middle of the board easy enough or on the rider.
However, if I understoood Mr. T’s statements of clarification correctly, the fin “reduces speed loss” through turns.
EDIT: If I am not mistaken, the GPS device measures speed relative to ground/bottom (horizontal speed vector). If so, this would reduce speed measurement values/readings in the vertical dimension (up & down).
When is someone going to jump in the deep end and fit accelerometers to their board? Give us real data.
Then whoever does it can prove all of us right or wrong. GPS is sort of only part of the equation.
Till then everyone’s opinion, including mine, is just that, an opinion, and the experience I used to come to my conclusion over the years was good enough for me. Have fun with your own!
Yes. If the GPS can only measure speed with reference to the ground (horizontal motion), it has significant limitations. Dropping straignt down the face or traveling straight up the face will read as almost zero/no speed.
Will the accelerometer distinguish between centripetal acceleration and gravitational acceleration, change in direction vs. change in speed?
Regarding opinions, after 287 years, I am satisfied that Newtonian physics has been sufficiently confirmed, and is no longer opinion.
That, and whether you can make outrageously fast waves. Example: 20 foot Makaha, from the point, big 15 foot Laniakea from deep at the point, 10 foot Pipeline from so deep, my excape was to go right if the left was closing out. That was in 1963, before ‘‘Backdoor’’ was even being ridden. The exceptional speed of my board, was in a large part due to the well foiled one inch thick walnut fin. The fin was 6.25 inches deep, with a 10 inch base. When you ride those kind of waves, your senses are so heightened, that the world seems to go into slow motion. You can observe quite bit, in a few seconds. No brag, just facts.
Fit an accellerometer to the tip of the tail, just to find board acceleration. Some people may be interested in how fast a nose whips around, but that’s irrelevant to actual board acceleration.
